180 [Assembly 



of the Iron Hill range of schist, about two miles west of Towner's. 

 Here the garnetiferous, micaceous and quartzose schist crops out 

 within 90 feet, horizontally of the light grey, fine crystalline gneiss, 

 approaching a grauulyte in composition and massive structure. The 

 former dips 60^-65° north, 5° west (magnetic), and the latter shows 

 a conformable bedding so far as any stratification is recognized in the 

 mineral arrangement of its mass. Going a short distance south-east 

 the strike changes to north-east and the dip is steep to south-east. 

 Passing around the head of the little valley and to the east side of the 

 same the grey gneiss forms the ridge on the east and at the foot and 

 close to the meadow, the schistose outcrop appears, with west-north- 

 "west dipping strata, and passing, apparently, under the little lime- 

 stone tongue in the bottom of the vallc}'. 



From the synclinal fold to be seen in the limestone outcrop at 

 its south-west end and the opposite dips in the schists on each side 

 it is evident that there is here a great synclinal, which includes the 

 schist as well as the overlying limestone ; and tlie base is the uncon- 

 formable grey, gramdytic gneiss. About a half a mile north-east of 

 Towner's the gneiss forms the base of an almost vertical wall of rock, 

 whose upper portion is a drab-colored, fine-granular sandstone. The 

 dip of the gneiss is 70° easterly: that of the sandstone is at an average 

 angle of 30° only, also eastward. Within one-quarter of a mile to east 

 there is a succession of gneiss, syenite-gneiss, micaceous gneiss and a 

 micaceous quartzite, each forming distinct ledges, or low ridges on a 

 section line which runs north 35° east (magnetic), and having about 

 the same angle of dip — 40° nearly. Unless overturned, which con- 

 dition seems impossible, the order of succession at this place gives a 

 key to the structure of the region; and it is in harmony with the order 

 observed at many other localities in the Archa?an rocks border. 



The discussion of the structure of the Archaean rocks of the High- 

 lands belt is deferred to a final report after a careful survey of the 

 whole terrain shall have been made. Many observations have been 

 made on the strike and dip of the strata along the Hudson river from 

 Peekskill to Fishkill, and from Poughquag in Dutchess county to 

 Brewsters in Putnam county and thence south-west to the Hudson. 

 Shorter sections also have been followed and the phenomena of out- 

 crops noted. The surface configuration and barometric measurements 

 of heights have received some attention. So far as the observations 

 go, they show a prevailing steep east-south-east dip, and a north-north- 

 east strike, that is obliqne to the trend of the belt, which is east-north- 

 east. The existence of an anticlinal fold of some magnitude is 

 indicated in the Fishkill range. As it involves an enormous thick- 

 ness to consider the formation as a single monoclinal series of strata, 

 the probable existence of close folds, with their axial planes dipping 

 very steeply to the cast-south-east, is inferred. And this hypothesis, 

 taken with a series of faulting planes runniftg, in general, north-east 

 and north-west courses, will explain most of the phenomena of struc- 

 ture which have been noted. 



The occurrence of unstratified outcrops of granitic and syenitic 

 rocks has been looked for, and two comparatively broad ranges have 

 been found ; one in the Fishkill monuntain range, and the other 

 east of Oregon, in Putnaui county. Areas of granitoid gneisses, or 

 granulyte-like gneisses, have been observed. The time of field-work was 

 altogether too short to trace out the contours of these characteristic out- 



